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Theorem peano2nn 7926
 Description: Peano postulate: a successor of a positive integer is a positive integer. (Contributed by NM, 11-Jan-1997.) (Revised by Mario Carneiro, 17-Nov-2014.)
Assertion
Ref Expression
peano2nn (𝐴 ∈ ℕ → (𝐴 + 1) ∈ ℕ)

Proof of Theorem peano2nn
Dummy variables 𝑥 𝑦 𝑧 are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 dfnn2 7916 . . . . . 6 ℕ = {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)}
21eleq2i 2104 . . . . 5 (𝐴 ∈ ℕ ↔ 𝐴 {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)})
3 elintg 3623 . . . . 5 (𝐴 ∈ ℕ → (𝐴 {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} ↔ ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)}𝐴𝑧))
42, 3syl5bb 181 . . . 4 (𝐴 ∈ ℕ → (𝐴 ∈ ℕ ↔ ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)}𝐴𝑧))
54ibi 165 . . 3 (𝐴 ∈ ℕ → ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)}𝐴𝑧)
6 vex 2560 . . . . . . . 8 𝑧 ∈ V
7 eleq2 2101 . . . . . . . . 9 (𝑥 = 𝑧 → (1 ∈ 𝑥 ↔ 1 ∈ 𝑧))
8 eleq2 2101 . . . . . . . . . 10 (𝑥 = 𝑧 → ((𝑦 + 1) ∈ 𝑥 ↔ (𝑦 + 1) ∈ 𝑧))
98raleqbi1dv 2513 . . . . . . . . 9 (𝑥 = 𝑧 → (∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥 ↔ ∀𝑦𝑧 (𝑦 + 1) ∈ 𝑧))
107, 9anbi12d 442 . . . . . . . 8 (𝑥 = 𝑧 → ((1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥) ↔ (1 ∈ 𝑧 ∧ ∀𝑦𝑧 (𝑦 + 1) ∈ 𝑧)))
116, 10elab 2687 . . . . . . 7 (𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} ↔ (1 ∈ 𝑧 ∧ ∀𝑦𝑧 (𝑦 + 1) ∈ 𝑧))
1211simprbi 260 . . . . . 6 (𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} → ∀𝑦𝑧 (𝑦 + 1) ∈ 𝑧)
13 oveq1 5519 . . . . . . . 8 (𝑦 = 𝐴 → (𝑦 + 1) = (𝐴 + 1))
1413eleq1d 2106 . . . . . . 7 (𝑦 = 𝐴 → ((𝑦 + 1) ∈ 𝑧 ↔ (𝐴 + 1) ∈ 𝑧))
1514rspcva 2654 . . . . . 6 ((𝐴𝑧 ∧ ∀𝑦𝑧 (𝑦 + 1) ∈ 𝑧) → (𝐴 + 1) ∈ 𝑧)
1612, 15sylan2 270 . . . . 5 ((𝐴𝑧𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)}) → (𝐴 + 1) ∈ 𝑧)
1716expcom 109 . . . 4 (𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} → (𝐴𝑧 → (𝐴 + 1) ∈ 𝑧))
1817ralimia 2382 . . 3 (∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)}𝐴𝑧 → ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} (𝐴 + 1) ∈ 𝑧)
195, 18syl 14 . 2 (𝐴 ∈ ℕ → ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} (𝐴 + 1) ∈ 𝑧)
20 nnre 7921 . . . 4 (𝐴 ∈ ℕ → 𝐴 ∈ ℝ)
21 1red 7042 . . . 4 (𝐴 ∈ ℕ → 1 ∈ ℝ)
2220, 21readdcld 7055 . . 3 (𝐴 ∈ ℕ → (𝐴 + 1) ∈ ℝ)
231eleq2i 2104 . . . 4 ((𝐴 + 1) ∈ ℕ ↔ (𝐴 + 1) ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)})
24 elintg 3623 . . . 4 ((𝐴 + 1) ∈ ℝ → ((𝐴 + 1) ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} ↔ ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} (𝐴 + 1) ∈ 𝑧))
2523, 24syl5bb 181 . . 3 ((𝐴 + 1) ∈ ℝ → ((𝐴 + 1) ∈ ℕ ↔ ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} (𝐴 + 1) ∈ 𝑧))
2622, 25syl 14 . 2 (𝐴 ∈ ℕ → ((𝐴 + 1) ∈ ℕ ↔ ∀𝑧 ∈ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦𝑥 (𝑦 + 1) ∈ 𝑥)} (𝐴 + 1) ∈ 𝑧))
2719, 26mpbird 156 1 (𝐴 ∈ ℕ → (𝐴 + 1) ∈ ℕ)
 Colors of variables: wff set class Syntax hints:   → wi 4   ∧ wa 97   ↔ wb 98   = wceq 1243   ∈ wcel 1393  {cab 2026  ∀wral 2306  ∩ cint 3615  (class class class)co 5512  ℝcr 6888  1c1 6890   + caddc 6892  ℕcn 7914 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-io 630  ax-5 1336  ax-7 1337  ax-gen 1338  ax-ie1 1382  ax-ie2 1383  ax-8 1395  ax-10 1396  ax-11 1397  ax-i12 1398  ax-bndl 1399  ax-4 1400  ax-17 1419  ax-i9 1423  ax-ial 1427  ax-i5r 1428  ax-ext 2022  ax-sep 3875  ax-cnex 6975  ax-resscn 6976  ax-1re 6978  ax-addrcl 6981 This theorem depends on definitions:  df-bi 110  df-3an 887  df-tru 1246  df-nf 1350  df-sb 1646  df-clab 2027  df-cleq 2033  df-clel 2036  df-nfc 2167  df-ral 2311  df-rex 2312  df-v 2559  df-un 2922  df-in 2924  df-ss 2931  df-sn 3381  df-pr 3382  df-op 3384  df-uni 3581  df-int 3616  df-br 3765  df-iota 4867  df-fv 4910  df-ov 5515  df-inn 7915 This theorem is referenced by:  peano2nnd  7929  nnind  7930  nnaddcl  7934  2nn  8077  3nn  8078  4nn  8079  5nn  8080  6nn  8081  7nn  8082  8nn  8083  9nn  8084  10nn  8085  nneoor  8340  fzonn0p1p1  9069  expp1  9262  resqrexlemfp1  9607  resqrexlemcalc3  9614  sqrt2irr  9878
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